Surgical instruments for shaping spinal endplates

ABSTRACT

The present invention relates to surgical instruments particularly suitable for preparing vertebral endplates during spinal interbody surgical procedures. Methods of using such instruments are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/973,481, filed Oct. 26, 2004, the entirety of which is incorporatedherein.

FIELD OF THE INVENTION

This invention relates to surgical instruments and methods of using suchinstruments. The instruments are particularly suitable for preparingvertebral endplates during spinal interbody implant procedures.

BACKGROUND OF THE INVENTION

In the simplest terms, the spine is a column made of vertebrae anddiscs. The vertebrae provide the support and structure of the spinewhile the spinal discs, located between the vertebrae, act like cushionsor “shock absorbers.” These discs also contribute to the flexibility andmotion of the spinal column. Over time, the discs may become diseased,infected, develop deformities such as tears/cracks, or simply losestructural integrity, for example, bulge or flatten. These impaireddiscs can affect the anatomical functions of the vertebrae, due to theresultant lack of proper biomechanical support, and are often associatedwith chronic back pain. Chronic back pain afflicts a large percentage ofthe world's population and often interferes with one's abilityparticipate in regular daily activities.

Several surgical techniques have been developed to address spinaldefects, such as disc degeneration and/or deformity. Spinal fusion hasbecome a recognized surgical procedure for restoring biomechanical andanatomical integrity to the spine. Spinal fusion techniques involve theremoval, or partial removal, of at least one intervertebral disc andpreparation of the disc space for receiving an implant by shaping theexposed vertebral endplates, an implant is then inserted between theopposing endplates. Vertebral endplates can have complex shapes due tovarious anatomical and biological factors. For example, a vertebralendplate may be concave in some portions. The vertebral endplates mayalso have surface irregularities and even bony protuberances, orosteophytes, which can be difficult to remove. These osteophytes, foundpredominately about the posterior-lateral portions of the endplate, areespecially problematic as they can painfully impinge on nearbyanatomical structures and reduce the useable implant-seating surface toprimarily the medial-anterior portion of the disc space. This reductionin seating area may compromise biomechanical integrity by reducing thearea in which to distribute mechanical forces, thus increasing theapparent stress experienced by both the implant and vertebral endplate.

Proper endplate preparation is important to successful spinal fusionsurgery procedures. To achieve fusion, it is generally necessary toexpose bleeding endplate bone stock. This initiates the biologicalhealing process of the bone and encourages implant integration. Thesurgeon must also conform or shape the endplate to, at least,approximate the implant geometry thereby ensuring proper seating of thespinal implant in the disc space. One of the many challenges ofpreparing the endplates is the discrepancy between the shape of theendplates and the implant. While the spinal endplates may have a complexsurface topography, the mating surfaces of spinal implants are generallyflat. Thus, the surgeon may initially desire to provide the maximumsurface area for proper implant seating by simply razing enough endplatebone stock to ensure a relatively flat surface.

In addition to maximizing the surface area available for implantseating, the surgeon should also preserve as much surface vertebralendplate bone as possible by minimizing the amount of bone removed sincethis subchondral bone is generally much stronger than the underlyingcancellous bone. Preservation of the endplate bone stock ensuresbiomechanical integrity of the endplates and minimizes the risk ofimplant subsidence. Thus, the surgeon should provide for optimal seatingof the implant while still maximizing the amount of available securingendplate bone stock.

The surgeon may rely on a number of instruments during complex spinalsurgical procedures. With the advent of spinal fusion surgery and thedevelopment of spinal implants, there is an increasing need forcomplimentary instruments. These complimentary instruments should reducethe “instrument load” on the surgeon while increasing the efficiency andprecision of the surgical procedure. These instruments should alsocompliment the final size and shape of the implant to be used; againincreasing the efficiency of the surgical procedure, while decreasingthe overall need for multiple instruments. While there are manyinstruments that may be required for such complex spinal surgicalprocedures, there is a need in the art for a single instrument suitablefor preparing vertebral endplates to properly receive a spinal implantfor spinal surgery procedures.

Methods of endplate preparation have traditionally been performed“by-hand” using a variety of instruments. Traditional free-handinstruments such as box chisels, osteotomes, curettes, drills, millinginstruments and the like, which aid in shaping the endplate, alsoaggressively, and sometimes unevenly, remove bone. Even when used by themost skilled surgeons, these traditional free-hand instruments may provedifficult to control in order to achieve uniform and reproducibleresults during endplate preparation. The surgeon must also avoiddamaging nearby anatomical structures, such as the spinal cord orvertebral arteries. These previously known “by-hand” methods andinstruments are generally cumbersome, lack precision, and may lead tothe removal of excessive amounts of vertebral endplate bone stock.

None of these approaches provide a single multi-purpose surgicalinstrument, as is now taught, for allowing controlled and precisepreparation of vertebral endplates while preserving endplate bone stock.Thus, there is a need in the art for a single spinal surgical instrumentwhich reduces the instrument load and the number of operating steps fora surgeon, improves visualization of the disc space while minimizingexposure of the disc space, and improves surgical safety by increasingthe precision of complimentary free-hand instruments while reducing therisk of damage to nearby anatomical structures.

There is a further need in the art for an instrument for the improvedpreparation of spinal endplates, especially one which can be used toprepare the posterior-lateral regions of the endplates and/or the entireendplate. There is also a need for a single instrument that can beflipped about its longitudinal axis outside of the disc space, andre-inserted to address features of both the left and rightposterior-lateral regions of a vertebral endplate. For example, a singlemulti-purpose instrument capable of preparing both the lateral andcontra-lateral sides of a vertebral endplate. Still further there is aneed for a single instrument capable of preparing both the left andright posterior-lateral regions of vertebral endplates and for removingosteophytes.

SUMMARY OF THE INVENTION

The present invention is directed to surgical instruments and methods ofusing such instruments. The instruments are particularly suitable inspinal surgeries for preparing a vertebral endplate during an anteriorapproach procedure.

Certain preferred embodiments of the present invention provide forprecise and controlled preparation of vertebral endplates usingfree-hand surgical instruments. Certain preferred embodiments of thepresent invention also provide for improved safety in addressingfeatures of the vertebral endplate posterior-lateral regions, includingthe removal of posterior-lateral osteophytes. Still other preferredembodiments allow for improved visualization of the disc space duringsurgical procedures while minimizing exposure of the operating space.

Certain embodiments of the present invention include a surgicalinstrument having both a rasp and a guide body. The instrument has agenerally D-shaped first portion which is longitudinally offset from,and connected to, a generally rectangular shaped second portion. Thefirst portion serves as a rasp, while the second portion includes anaccess port that serves as a device guide. As used herein, a device foruse in accordance with certain embodiments of the present invention maybe, without limitation, any free-hand instruments including a reamer,box chisel, osteotome, curette, drill, milling instrument or the like,which aid in preparing vertebral endplates. The second portion may alsoinclude any number of housings or structures capable of guiding a devicesuch as, for example and without limitation, through-holes, accessports, frames, carriages, tracks, etc. Still further, the device may becontrollably advanced along the longitudinal axis of the second portion.The second portion may further include a threaded opening for attachmentto a threaded holder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a perspective view of an embodiment of one surgicalinstrument of the invention (10) having a generally D-shaped firstportion (20) and a second portion (30). FIG. 1B further depicts a topview of the same embodiment. Lastly, FIG. 1C depicts a side view of theembodiment showing a transverse aperture (50) of the D-shaped portion(20).

FIG. 2A is a perspective view of an embodiment of the surgicalinstrument (10) having a contact member (90). FIG. 2B further depicts anembodiment having a contact member only on the upper surface, while FIG.2C depicts contact members (90) on both the upper and lower surfaces.

FIG. 3A depicts a top view of an embodiment of the surgical instrument(10) configured to accept a reamer (200) though device guide (80). FIG.3B depicts a side view of the surgical instrument (10) showingvisualization of the reamer through the transverse aperture (50).

FIG. 4 illustrates a perspective view of an embodiment of the surgicalinstrument (10) configured to accept a box chisel (300).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Certain presently preferred aspects of the present invention may be usedfor the preparation of spinal endplates for a variety of interbodyimplant procedures. These procedures include, but are not limited to,spinal fusion, vertebral body replacement, and artificial discprocedures. Thus, certain embodiments of the present invention aredirected to an instrument and method for use in spinal surgeryprocedures. Certain embodiments of the surgical instrument areparticularly suitable for procedures in which an implant is placedbetween adjacent vertebrae, such as in spinal fusion procedures, orthose which use an implant to replace all or part of one or morevertebral bodies such as during vertebral body replacement procedures.For either procedure, stability of the implant is a major concern, thusimplant loosening and/or motion should be avoided as either conditionmay impair implant performance, result in anatomical damage, presentsubstantial pain to the patient, and may result in implant expulsionfrom the disc space. As such, proper preparation of the disc space and,particularly, the spinal endplates is critical.

In accordance with certain embodiments of the present invention, asurgical instrument is provided comprising both a rasp and a deviceguide. As shown in FIG. 1, the instrument (10) includes a generallyD-shaped first portion (20) which is longitudinally offset, andconnected, to a generally rectangular shaped second portion (30). Theposterior-lateral-most aspect of the first portion (20) is rounded suchthat its contour matches the posterior-lateral aspects of the interbodyimplant for good conformity. Both the top and bottom surfaces of thefirst portion include rasp (40) for endplate preparation. Alternatively,first portion (20) may have a rasp (40) on either the top or bottomsurfaces. Rasp (40) may cover any degree of the top and/or bottomsurfaces, but preferably cover the entire top and bottom surface of thefirst portion. The first portion (20) also includes an aperture (50)that extends the entire transverse length of the first portion (20),thus the first portion may be predominantly hollow. Alternatively, firstportion 20 may include a plurality of apertures (50) having uniform orvaried size/shape. These apertures (50) aid in the fluoroscopicvisualization of a device, such as reamer (200), during a surgicalprocedure as either an embodiment of the surgical instrument of thepresent invention or a reamer is advanced into the disc space. Thesecond portion (30) includes a threaded opening (60) on the mostproximal end surface, or front face, (70) for attachment to a threadedholder (not shown). The second portion (30) also includes an access portthat serves as a device guide (80) adjacent the threaded opening (60).Device guide (80) is particularly useful for controlling the trajectoryof free-hand devices, thus increasing the precision of the surgicalprocedure while also providing for controlled removal of bone in theposterior-lateral regions. First portion (20) may be substantiallyplanar or substantially cylindrical. First portion (20) may also act asa stabilizing element in reducing vibration, and other unwantedmovement, while improving free-hand instrument balance and precision.First portion (20), including rasp portion (40), may further serve as astandard rasp for initial preparation and roughening of the vertebralendplate surface with minimal bone removal. The surgeon may thereforechoose to skip an initial rasping step using a standard free-hand rasp,and may instead use certain embodiments of the present invention forrasping as well as targeted bone removal. The first portion and/orsecond portion may also have at least one graded marking or measurement,to gauge the depth of penetration into the disc space.

Certain embodiments of the present invention may also include at leastone raised shoulder or contact member (90). The contact members may beany variety of sizes or shapes, so designed to abut at least oneadjacent vertebral body. The contact members may also be slidably and/orrotatably connected to second portion (40). Still further, contactmember (90) may be extendable to abut a plurality of adjacent vertebrae,as needed. Contact member (90) may be particularly useful in preventingor minimizing damage to nearby anatomical structures.

Preferred embodiments of the present invention are particularly suitedfor shaping the lateral aspects of the posterior portion of theendplate. The instruments of the present invention can be used with avariety of implants. In particular, those implants having a generallyannular shape with rounded corners, for example elliptical or “D”shaped, may be used in accordance with the present invention. In stillother preferred embodiments of the present invention device guide (80)may be used with a reamer. In use, a reamer (200) is inserted throughthe device guide (80) and used to precisely shape the lateral aspects ofthe posterior portion of the endplate to match the correspondinggeometry of the implant. The reamer also aids in the removal ofposterior osteophytes and may be provided with a depth control featuresuch as collet or shoulder to prevent the reamer from breaching the discspace and damaging nearby anatomical structures. For the remainder ofthe endplate preparation, the rasp portion (40) of the instrument (10)is used. Thus, the present invention allows easy and precise reaming ofthe lateral corners of the posterior endplate, while at the same timeprovides a rasp for preparing the remainder of the endplate. Theinstrument can be flipped 180° about the longitudinal axis of deviceguide (80) (an imaginary line which runs orthogonal to the front face(70) of the instrument (10) to the distal end of the instrument andwould run parallel to the longitudinal centerline of an inserted reamerdevice). In this manner, the instrument can first be used to prepare theleft side of the endplate, removed from the disc space, rotated 180°,and re-inserted to the disc space to prepare the right side of theendplate. This “flipping” action is particularly convenient in caseswhere there are posterior-lateral osteophytes which require removalprior to preparing the disc space. Thus, certain preferred embodimentsof the present invention can be flipped to remove osteophytes on bothsides of the endplate, then used to properly ream and prepare the discspace.

In certain embodiments of the present invention, the second portion (30)may also include a threaded opening (60) on the most proximal endsurface, or front face, (70) for attachment to a threaded holder (notshown). Still further, second portion (30) may be removably attached toa holder by a variety of engagement structures including, but notlimited to, interlocking components or snug-fit mating components. Inother embodiments, the present invention is integral with a holder (notshown). And yet in other embodiments, the first portion (20), secondportion (30), and holder are all modular components that are assembledduring surgery.

In still other embodiments of the present invention, second portion mayalso include any number of housings or structures capable of guiding adevice such as, for example and without limitation, through-holes,access ports, frames, carriages, tracks, etc. Embodiments of deviceguide (80) may be any number of shapes including, circular, rectangular,irregular, or custom shaped to particular device. Still further, thedevice may be controllably advanced along the longitudinal axis of thesecond portion. The second portion may further have any number ofmechanisms or structures which facilitate controllable deviceadvancement therefrom. For example, and without limitation, the secondportion (30) may contain a threaded access port (80) to accept athreaded reamer; a track, carriage or frame that may be controllablyextended from the second portion; an access port (80) having an internalratchet or other stop-motion mechanism operatively engaged with areamer; and/or a telescoping access port (80). Thus, second portion (30)may provide for controlled reamer (200) advancement, and controlledreaming depth, into the disc space. Controlled depth of reaming may beparticularly useful in preventing, minimizing or even eliminating damageto the surrounding anatomical structures. An alternate embodiment of thepresent instrument may be configured for use with a free-hand boxchisel, or similar instrument. In this manner, access port (80) ofsecond portion (30) serves as a device guide for improved safety,uniformity, and precision of a chisel device.

Embodiments of the present surgical instrument are preferably made of adurable material such as stainless steel, stainless steel alloy,titanium, or titanium alloy, but can also be made of other durablematerials such as, but not limited to, polymeric, ceramic or compositematerials. Durable materials may also consist of any number of puremetals and/or metal alloys. Certain embodiments of the present inventionmay also include more than one material. For example, the first portionmay be made of a metal alloy and the second portion may be made of aceramic material.

Certain preferred embodiments of the present invention may include arasp portion (40) of various sizes. In certain embodiments of theinvention, modular rasp portion (40) may be provided in varying sizes,shapes, and/or degrees of coarseness, which may be connected to theremaining modular components during surgery. For example, first portions(20) of various size, etc. may be removably connectable to a single basesecond portion (30), or alternatively may be assembled to various secondportions (30). In yet still another embodiment, there may be multiples,or series, of instrument (10) each having a rasp portion (40) of varioussizes, or shapes and/or degrees of coarseness, which are made availableduring surgery. Still further, rasp portion (40) may act as a spacer tomaintain a desired intradiscal height while the lateral aspects of theendplates are prepared to a desired shape using a reamer or othersuitable tool. Thus, the entire spinal endplate final geometry can beconveniently prepared to match a desired implant geometry for optimalseating of the implant in the disc space.

Different sizes of rasp portion (40) may cover various percentages ofthe available medial-lateral disc space. For example, one embodiment ofrasp portion (40) may cover the entire medial-lateral width of the discspace. While other embodiments of rasp portion (40) may cover 50%, ormore, of the medial-lateral width of the disc space with the remainderof the instrument serving as a guide for a reamer designed particularlyfor preparation of the spinal endplate, including removal ofposterior-lateral osteophytes in the disc space. In yet anotherembodiment of the present invention, the entire width of the instrumentis equivalent to the entire width of the implant to be inserted.

EXAMPLE

A certain embodiment of the present invention was used to prepare spinalendplates to receive a vertebral body replacement. In this surgicalprocedure, the spine was first exposed via an anterior approach and thecenter of the target disc was identified. The anterior annulus was thenremoved and a complete discectomy was performed. Residual cartilage wasremoved from the spinal endplates to expose bleeding bone. The resultantdisc space was distracted by impacting sequentially larger heights ofdistractors/trial spacers into the disc space, until a tight feel wasobtained.

Spinal endplate preparation started with a standard general rasp whichwas impacted into the disc space for initial coarse rasping and thenremoved. A size-specific rasp-reamer guide instrument (10) of thepresent invention was then used to remove strong osteophytes in theposterior-lateral region of the spinal endplate. The size specificrasp-reamer guide instrument (10) was impacted into the disc space viathe end face of an optional instrument holder connected via opening(60).

A size-specific reamer (200) was advanced through the opening (80) ofsize specific rasp-reamer guide instrument (10), under fluoroscopicguidance, to remove posterior osteophytes on one side. A size-specificreamer (200) and rasp-reamer guide instrument (10) were then removedfrom the disc space. The rasp-reamer guide instrument (10) was thenflipped about 180° about the longitudinal axis of reamer guide (80), andthe previously discussed steps were repeated for the contra-lateral sideof the spinal endplate.

After adequately preparing the endplates, the appropriately sizedimplant was selected, packed with graft material and placed in theprepared disc space.

Those skilled in the art will appreciate that numerous changes andmodifications can be made to the many embodiments of the invention andthat such changes and modifications can be made without departing fromthe spirit of the invention. It is therefore intended that the appendedclaims cover all such equivalent variations as falling within the truespirit and scope of the invention.

1. A surgical instrument for use in spinal surgery comprising alongitudinal axis and a first portion and a second portion; wherein saidfirst portion and second portion are longitudinally offset from eachother and a section of the proximal end the first portion is connectedto a section of the distal end of the second portion; said first portionis generally D-shaped in a transverse cross-section and furthercomprises a top and bottom surface having rasp teeth; said first portionfurther including at least one aperture that extends the entiretransverse length of said first portion; said second portion has agenerally rectangular shaped body and comprises an access portionextending parallel to the longitudinal axis of the instrument andextending through the body of the second portion; said second portion isadapted for removable attachment to a holder; and wherein the instrumenthas a transverse axis orthogonal to the longitudinal axis and the firstand second portions have a substantially equivalent width along thetransverse axis of the instrument.
 2. The surgical instrument of claim1, wherein at least one of said first and second portion furthercomprises at least one contact member.
 3. The surgical instrument ofclaim 2, wherein said at least one contact member is extendable from atleast one of said first and second portion.
 4. The surgical instrumentof claim 1, wherein said instrument is comprised of a durable material.5. The surgical instrument of claim 4, wherein the durable material isat least one of a pure metal and metal alloy.
 6. The surgical instrumentof claim 1, wherein the access port is a device guide.
 7. The surgicalinstrument of claim 6, wherein the device guide is adapted to control afree-hand device for shaping vertebral endplates selected from the groupconsisting of a reamer, box chisel, osteotome, curette, drill, andmilling instrument.
 8. The surgical instrument of claim 1, wherein theadaptation of the second portion for removable attachment to a holder isa threaded opening on the proximal end of the second portion.
 9. Thesurgical instrument of claim 8, wherein the threaded opening is parallelto the longitudinal axis of the instrument.
 10. The surgical instrumentof claim 1, wherein the access port is cylindrical.
 11. A surgicalinstrument for use in spinal surgery comprising a longitudinal axis anda first portion and a second portion; wherein said first portion andsecond portion are longitudinally offset from each other and a sectionof the proximal end of the first portion is connected to a section ofthe distal end of the second portion; said first portion is generallyD-shaped in a transverse cross-section and further comprises a top andbottom surface having rasp teeth; said first portion further includingat least one aperture that extends the entire transverse length of saidfirst portion; said second portion have (a) a generally rectangularshaped body, (b) a device guide extending parallel to the longitudinalaxis of the instrument and extending through the body of the secondportion, and (c) an opening extending parallel both to the longitudinalaxis of the instrument and to the adjacent device guide, extending atleast part-way through the body of the second portion, and being adaptedfor removable attachment to a holder; and wherein the instrument has atransverse axis orthogonal to the longitudinal axis and the first andsecond portions have a substantially equivalent width along thetransverse axis of the instrument.
 12. The surgical instrument of claim11, wherein the device guide is adapted to control a free-hand devicefor shaping vertebral endplates selected from the group consisting of areamer, box chisel, osteotome, curette, drill, and milling instrument.13. The surgical instrument of claim 11, wherein the opening of thesecond portion is a threaded opening.
 14. The surgical instrument ofclaim 11, wherein the device guide is cylindrical.
 15. The surgicalinstrument of claim 11, wherein at least one of the first and secondportion further comprises at least one contact member.
 16. The surgicalinstrument of claim 11, wherein the instrument is comprised of a durablematerial selected from at least one of a pure metal and a metal alloy.17. A surgical instrument for use in spinal surgery comprising alongitudinal axis and a first portion and a second portion; wherein saidfirst portion and second portion are longitudinally offset from eachother and a section of the proximal end of the first portion isconnected to a section of the distal end of the second portion; saidfirst portion is generally D-shaped in transverse cross-section andfurther comprises a top and bottom surface having rasp teeth; said firstportion further including at least one aperture that extends the entiretransverse length of said first portion; said second portion has (a) agenerally rectangular shaped body, (b) a cylindrical device guideextending parallel to the longitudinal axis of the instrument, extendingentirely through the body of the second portion, and being adapted tocontrol a free-hand device for shaping vertebral endplates selected fromthe group consisting of a reamer, box chisel, osteotome, curette, drill,and milling instrument, and (c) an opening extending parallel both tothe longitudinal axis of the instrument and to the adjacent deviceguide, extending at least part-way through the body of the secondportion, and being adapted for removable attachment to a holder, whereinthe instrument is made of a durable material and has a transverse axisorthogonal to the longitudinal axis, and the first and second portionshave a substantially equivalent width along the transverse axis of theinstrument.
 18. The surgical instrument of claim 17, wherein at leastone of the first and second portion further comprises at least onecontact member.